Here's a quick and easy one. For all I know, you might have all kinds of reasons as to why you want to have your links to open in new tabs. If I had to guess, I'd say you want your readers to keep exploring/crawling your blog while always having a chance of going back to the the referring page (where they came from).
You have a higher chance of keeping your readers in your blog if your blog pages are opened in multiple tabs. If all your links open in a single tab, how many of your readers will actually hit the 'back' button to go back to your main page and check your other posts and links? When you make your links open in a new tab, you force your readers to somehow go back to your main page.
All reasons aside, here's how you can do it.